You’ve shot the perfect interview. The subject was animated and interesting. Your lighting and camera work were the best yet and you can’t wait to edit the footage. However, during the capture session, you hear something that concerns you – your masterpiece sounds hollow. How can this be? You used your best microphone and all the connections were perfect. What happened?
Unfortunately, you’ve fallen victim to poor room acoustics and no amount of processing in the world can completely repair the empty, distant sound on your recording. While you can’t fix the damage, you can avoid similar problems in the future. Let’s explore what makes rooms sound the way they do and what, if anything, you can do to optimize them for audio recording.
Shape Shifter
The primary variable that determines the sonic characteristics of a room is its shape. The majority of rooms you’ll encounter are either square or rectangular in shape. However, on occasion, you will find other shapes such as hexagons, octagons and even a round room from time to time. The main thing to remember is that each of these shapes affects the sound character of the room differently. A rectangular room will sound very different from one with an octagonal shape. Round rooms (such as the dome of an observatory) can be acoustically disorienting as sounds reflect and amplify, seemingly to coming from behind you, even with your back to the wall. Don’t forget to factor in the ceiling, whether flat or vaulted, and any other unique architectural additions such as alcoves and nooks.
Rooms with parallel walls (the most common situation) produce standing waves of sound. This phenomenon is easily demonstrated by centering yourself between the two walls and clapping your hands. You will likely hear a quick series of echoes with each handclap. These are called "flutter echoes" and can ruin a recording if allowed to creep into your microphone. I once did some work in a large geodesic dome building and, while its architecture was awe inspiring, the room acoustics were challenging to say the least. In virtually every location, there was some sort of echo. The liveliness of the sound reminded me of a racquetball court. Needless to say, it was not designed for acoustic appeal. Pay attention to the shape of the room and listen closely to how that configuration molds the sound of your subject.
Another Dimension
In addition to the shape of the room, its relative dimensions also play a key factor in the acoustic quality you’ll hear. Acoustical engineers use principals called "golden ratios" – mathematical ratios of length, width and height – to determine room dimensions that produce a pleasing sound . Used on everything from home theaters to concert halls, these golden ratios are proven ways to create an acoustic space that works well with both natural and amplified sound. This works by minimizing the effects of another acoustic issue called "room modes." Room modes occur in the lower frequencies and often make a room sound boomy or bass-heavy. Certain room dimensions can produce problems with the distribution of sound in the room and often result in hot spots that contain a significant buildup of sound energy in certain tonal ranges.
Of course, you aren’t designing the rooms you’ll shoot in, but an understanding of basic design principles will increase your ability to capture good audio during the shoot.
Decorator’s Touch
After the shape and dimensions of a room have been established, furnishings and floor coverings also play a key element in room sound. The finish of a room’s floor has more to do with its sound character than any other item. A tile or concrete floor is very hard and reflective. Consequently, sound bounces off the floor easily and will continue to reflect off every hard object in the room until it dissipates. However, a floor covered with an area rug – or better, carpet – will absorb sound to varying degrees and minimize the effects of reflected sound. As an added bonus, it will also minimize background noises from shuffling feet and moving furniture.
Furnishings also play a role in the acoustic signature of a room. A large, overstuffed couch with big pillows will absorb a great deal of reflected sound, while a hardwood dining table and chairs will reflect more of that sound. Reflection isn’t all bad, though. Recording studios spend a great deal of time and money installing controlled sound reflectors or diffusers. These specialized devices scatter reflected sound in a special way that reduces the ill effects while maintaining even dispersion.
What Can I Do About It?
Unless you carry a truck full of acoustic treatment products, there is little you can do to affect the audible attributes of the room you’re shooting. However, there are several things you can do to tip the scales in your favor.
First, scout the room prior to the shoot and listen carefully to the sound of speech in your preferred location. If there is a significant amount of echo or liveliness to the sound, try to secure another locale. If another venue isn’t available, look for the best position in your room of choice. Sometimes, moving just a few feet produces a dramatic change in sound.
There is another acoustic phenomenon call a "suck-out." This is a place in a room where all sound seems to disappear to some degree. Of course, you probably won’t find one where you want or need it, but have someone speak as you walk around the room. You may find a position that contains less reflections and better sound quality.
If you must work in an acoustically live room, use a lapel microphone instead of a shotgun. A lapel microphone can be positioned closer to the mouth of the subject and uses the person’s body to block sound reflections from other parts of the room. If you must use a shotgun microphone, position it as close to the subject as possible and consider a few alternate positions if your headphones tell you there is too much echo.
Finally, several companies offer temporary acoustic treatment products. These take the form of sound absorbing blankets, acoustic foam, insulated panels and stand-mounted sound absorbing devices. Large television and film production units often set these items up for each shoot, just outside the video frame. The results can be quite dramatic and prices have come down in recent years. As just one example, we found 68-inch x 76-inch sound blankets for less than $20 each at Markertek.
You’ve probably guessed by now that an acoustically "dead" room is preferable to a "live" one. The reason is simple – it’s practically impossible to extract ambience from your recording, and it’s very easy to add acoustic character to your audio during post-production through reverb and other digital effects, while it is nearly impossible to remove unwanted echoes and reverb.
Armed with your newfound knowledge of room acoustics, you will definitely be able to record better audio the next time you shoot.
Sidebar: Room With A View
Every room has a unique sonic signature. While this can work to your benefit, it more often results in less-than-ideal recordings. Listen closely to the rooms you shoot in and you’ll quickly recognize some of the common traits. For instance, a large open living room may sound dead if it has carpet and overstuffed furniture, but may sound live if it has hardwood floors and sparse furnishings. Bedrooms are often small and boxy, with similar dimensions for height, width and length. These dimensions translate directly to its sonic character. Bathrooms often have tile on the floor and even the walls. That, along with all the porcelain and glass makes for a very bouncy acoustic environment.
Sidebar: DIY Soundproofing
Recording narration and voiceovers is a challenge, even with the right equipment. One of the most important recording tools is the room you record in. Not just any room will do since the ill effects of shape and furnishings can make your voiceover sound amateurish. Your first option is to find a walk-in closet full of clothes. Although cramped, this is an ideal recording environment from an acoustic standpoint. As they say, the deader, the better. Alternatively, you can sound proof a room for recording by hanging thick, padded objects on the walls – such as sleeping bags, comforters or moving blankets. Carpet scraps and even egg crates can all be used with amazing results.
